The present invention relates to a method and apparatus for producing molded thermoplastic parts having aspherical surfaces, using mold components with cavity-limiting surfaces. The method and apparatus of the invention have particular use in the manufacture of continuous-focus eyeglass lenses.
In known methods for molding thermoplastic parts, namely by injection-molding or compression-molding, particular importance must be placed on the molding-cavity surfaces being sufficiently rigid that the molded product is given precisely the form desired. This is particularly true when, to produce surfaces of optical quality it is necessary to operate with high pressure during the manufacturing process.
It is known that aspherical surfaces can be produced in the molding of thermoplastic parts. For this purpose, it has been the practice to provide corresponding aspherical surfaces in the mold cavity. The production of such complex surfaces is extremely expensive, due in particular also to the above-mentioned need for rigidity. Such production expense is particularly unfavorable in the manufacture of eyeglass lenses having aspherical surfaces, when a whole series of lenses of different dioptric powers is required, thus dictating the need for a very large number of different aspherical surfaces.